22 April 2007

Carbon Offsets -- Can They Help?

Carbon Offsets May or May Not Offset Any Carbon

photo of jet airliner from a NASA site
When you pay for a "carbon offset" the money goes to a company or non-profit project (maybe through a broker or other agent, who takes a cut). That company or project is doing something that sequesters carbon or generates low-carbon energy. The money it gets by selling offsets helps the economics of the project.

People often buy offsets because it is easier or cheaper for them to do so than to actually reduce the carbon their activities emit. For example, you may really want to take a plane trip. When that plane flys it emits CO2. (Of course, it would emit essentially the same amount of CO2 if you stayed home.) You can "offset" the carbon emissions your trip caused by arranging, for example, to reduce greenhouse gas emissions somewhere else.

The key to getting carbon offsets to make sense is: Whatever you buy when you buy the carbon offset must actually result in the absorption of the amount of CO2 you produce, or the substitution of energy made without emitting CO2 for carbon-intensive energy, or by capture of emissions that would have been released if you hadn't chipped in. But what if:
  • The trees would have been planted anyway, even if you had not bought the offset.
  • The trees are to be planted in a northern clime where they will absorb more winter sunlight than the snow they cover, thus actually increasing global warming in spite of the carbon they absorb? (See this study and these comments.)
  • The trees are planted in what was a tropical peat bog or forest, and more CO2 is emitted when planting them than they will ever absorb? (This study)
  • The electricity generated by the wind-power project you supported will not substitute for carbon-based power, but just add to it, driving down the price of electricity and encouraging consumption?


There are certification schemes to assure that at least some offsets don't have these problems. The key is that the projects provide "additionality". That means that they offer additional carbon reduction that wouldn't have been achieved without your purchase of an offset. Here is the complicated method used to determine additionality.

In general, if you want your carbon offsets to really reduce CO2 emissions, they should comply with the criteria established by The Gold Standard, which specifically excludes tree-planting and similar schemes, or other strict certification programs. This paper by Friends of the Earth, Greenpeace and WWF explains why.

How do you find an offset that will really reduce global carbon in a way that will make up for the greenhouse gasses you continue to produce? The Environmental Defense "Fight Global Warming" page lists some offset projects they have vetted.

But wouldn't it be better for you to actually reduce the amount of carbon your activities emit? At worst, carbon offsets provide a way for wealthy people to ease their consciences when they pursue carbon-intensive activities. At best, they compensate for those activities, so we come out even. The only way to come out ahead (that is, to actually reduce your carbon emissions) is to change your lifestyle.


Carbon offsets can help, but only if you do your homework. And they can't do the whole job.

Some questions:

  • Should new nuclear power plants be able to sell carbon offsets?
  • Currently, British Airways offers to arrange carbon offsets for its passengers (the passengers pay for them). Why doesn't it simply buy enough offsets to make the flight carbon neutral and add the cost to the price of the tickets? (Answer obvious: people would fly cheaper, carbon-positive flights with competitors.)
  • Could you make money setting up a gas station that bought carbon offsets to make all the fuel it sold carbon neutral, and added their cost to the cost of the gas? How much more would the gas cost? Would anybody buy it? (Business plan idea here -- maybe you could enter the California CleanTech Open and win $100,000.)
  • What if the legislature mandated that all gas stations do this, so that the cost of fuel would reflect its true environmental impact?

Here are some useful links:


David Suzuki Foundation has some good links

10 April 2007

How Green Is Ethanol?

ethanol corn logo from ISU Society of Automotive Engineers http://sae.stuorg.iastate.edu/formula/gallery/Sponsor-Pictures/corn_logo

Does Corn-Based Ethanol Help the Environment?

How much energy do you save if you run your car, truck or SUV on an ethanol blend instead of ordinary gasoline?
None. It takes the same amount of energy to move you and your vehicle no matter what form of fuel you use. The only way to save energy is to get a more efficient vehicle (that gets higher mileage) or to drive less.
How much fossil petroleum (oil) do you save if you run your car, truck or SUV on an ethanol blend instead of ordinary gasoline?
Not much. One gallon of corn ethanol displaces 0.67 gallons of gasoline. (Ethanol has 0.7 times the energy content of gasoline, and it takes about 0.03 gallons of petroleum fuels to make a gallon of ethanol from corn.) So if you use E10 (a blend of 10% ethanol with 90% gasoline) you would save 0.0028 gallons of fossil petroleum for every mile you drive (if you get 25 mpg). If you drive the U.S. average of 12,500 miles per year, you would reduce fossil petroleum consumption by close to 35 gallons. Per year. Total.

If you used E85 (85% ethanol and 15% gasoline, for which you would need a "flex-fuel" vehicle, which make up only 2% of the U.S. passenger and light truck vehicle fleet) you would save 0.28 0.03 gallons of fossil petroleum fuel for each mile you drive (if you got 18 mpg with E85--remember ethanol has less energy per gallon than gasoline. You'd have to buy about 15% more gallons to get through your yearly driving). For 12,500 miles a year, that is 3,700 395 gallons. If all the 4 million flex-fuel vehicles in the U.S. actually used E85 (less than 1% do), together they would reduce demand for gasoline from fossil petroleum by 15 million 1.6 billion gallons annually. That is about 0.014% 1.4% of total gasoline consumption in the U.S. (one one-hundredth of one percent). [Updated 2012-07-28]
How much greenhouse gas emissions do you save by using ethanol?
We don't know. If you use E10 you either increase greenhouse gas emissions by about 2%, or reduce them by about 2%, or somewhere in between, depending on how the greenhouse gas contributions of the byproducts of ethanol production from corn are accounted for. Basically, using E10 instead of gasoline cuts your greenhouse gas output by very little, and might even increase it a bit.

If you use E85, you either increase greenhouse gas emissions by about 20% or reduce them by about 20%, again depending on how you define the system boundaries. How much is a matter of opinion. Of course, practically nobody uses E85 – There are no E85 stations within 100 miles of Los Angeles, for example. (see E85 Refueling)


Do the math. If you want to reduce petroleum use and greenhouse gas emissions you have to change what you drive, how you drive, and how much you drive. Switching fuels won’t make much difference.

A principal source for the analysis above was Review of Corn Based Ethanol Energy Use and Greenhouse Gas Emissions. T. Groode. LFEE Working Paper 07-1, June 2006, from The Laboratory For Energy and the Environment at the Massachusetts Institute of Technology.

Good summary of Groode’s analysis in energy & environment, October 2006, the newsletter of the MIT Laboratory for Energy and the Environment.

03 April 2007

How Much Carbon Dioxide From Biodiesel

Biodiesel puts CO2 in the Atmosphere -- But How Much?

soybean plant, borrowed from http://technolog.it.umn.edu/technolog/spring2002/biodiesel.htmlBiodiesel is made from vegetable oil or animal fat. In the U.S., most of it is made from soybean oil. This makes it a "renewable" or "alternative" liquid transport fuel.

The carbon dioxide released by burning biodiesel in your vehicle was originally taken out of the air by soybean plants. So in some sense biodiesel is "carbon neutral" and doesn't contribute to increasing atmospheric CO2 as much as the regular diesel made from fossil petroleum.

To produce one gallon of biodiesel takes about 18 kg of soybeans. But the soybeans are only part of the soybean plants that produced them. The soybean harvest makes up only about one-quarter of the biomass of the soybeans the farmer grew. So the total biomass grown to make a gallon of biodiesel is about 75 kg.

The soybean plants made themselves out of air, using the energy in sunlight to fix CO2 into carbohydrates and lipids. Growing that 75 kg of soybean plants took about 175 kg of CO2 out of the air. (The plants spat the O2 out again, and replaced it with the lighter element hydrogen.)

So that gallon of biodiesel started off as 175 kg of CO2. To produce the soybeans, crush them to separate their oil, manufacture the oil into biodiesel, and transport the products among these operations took some energy derived from fossil fuels. Assuming this energy came half from natural gas and half from liquid fuels, these fuels contained 700 grams of carbon. When they were burned they released about 2.5 kg of CO2. (True, the transportation fuels could have been biodiesel -- the impact of such substitution is left to the student as an excercise.)

Where the Carbon Goes

So about 177 kg of CO2 is embodied in the gallon of biodiesel, and all of it will be released as the biodiesel is produced and used. Here is where it goes:
  • About 30 kg of plant residue is left in the field. Eventually it decomposes and releases 110 kg of CO2. This is more than 60% of the 177 kg of CO2 we started with.
  • Soybean oil makes up only about 18% of the soybean, by weight. After the oil is extracted what is left is "soybean meal", a valuable protein-rich animal feed. The Soybean meal from our one-biodiesel-gallon's worth of soybeans weighs about 15 kg and contains about 13 or 14 kg of carbon. Eventually it will be digested by animals, broken down, and converted back into CO2 (it may have to go through several animals to finally be CO2 again). That will yield about 53 kg of CO2, about 30% of what we started with.
  • When the soybean oil is converted into biodiesel there is some glycerine produced as a byproduct. When that glycerine is eventually broken down it will release another 850 grams of CO2 (less than 1%).
  • The fossil energy consumed in the growing, transporting, and processing to get biodiesel to the vehicle's fuel tank produces about 2.5 kg of CO2 (about 1.5%).
  • Finally we get to the biodiesel. One gallon of biodiesel has about 2.8 kg of carbon in it, and when it is burned it will produce about 10 kg of CO2. that is about 5.5% of the CO2 fixed by the soybeans and burned to make them into fuel.
picture of biodiesel-powered bus, by U.S. Department of Energy: Energy Efficiency and Renewable Energy

Efficiency of Biodiesel

So in one sense we used agricultural and industrial ingenuity to convert 700 grams of carbon in the form of fossil fuels into 2700 grams of carbon in biodiesel. That is like multiplying that fossil carbon 3.8 times!

On the other hand, the process was shockingly inefficient, turning 50 kg of carbon fixed by plants into 2.7 kg of carbon in liquid fuel form. Only 5.5% of the total fixed carbon ended up powering a vehicle!


It all depends on how you look at it.